Gearboxes can be used to increase torque while reducing the rotational speed of a shaft. For example, an output shaft may rotate at a slower speed than an input shaft. This speed reduction is can be effected by interfacing two or more gears with different numbers of gear teeth and may provide a mechanical advantage.
There are many ways to arrange gears so that a single rotation of a first gear will result in more or less than one rotation of a second gear in the same amount of time. The gear ratio is the ratio of these two rotations. In the case where the second gear rotates less than the first gear the gear combination could be said to provide a gear reduction. In certain applications it is desirable to have a gearbox with a relatively high gear ratio, where the gear reduction takes place in the smallest possible volume. For example, a drive mechanism that converts many rotations of an input shaft into a single rotation of an output shaft.
Historically, wobble plate drive mechanisms have seemed a promising route toward a device having a high gear ratio within a small volume. Examples of such wobble plate drive mechanisms are disclosed in U.S. Patent Publication Nos. US20140285072 and US20150015174. Older systems are disclosed in U.S. Pat. No. 2,275,827 and U.S. Pat. No. 3,249,776. The disclosures of these and all other publications referenced herein are incorporated by reference in their entirety for all purposes.
In a wobble plate mechanism, one of the gears, a wobble plate, nutates around another gear, for example a stator gear. If the number of gear teeth on the wobble plate and the stator gear are different by one, then such a system would have a gear ratio equal to the number of teeth on the stator gear.
In principle, the gear ratios in wobble plate drive mechanisms could be quite high. A theoretical wobble plate drive mechanism only using two gears may achieve a relatively high gear ratio, in a small volume. However, in practice, efficient and effective wobble plate drive systems have proved elusive, because the forces involved often lead to one or more of disengagement of the mechanism, unacceptable levels of vibration, or inefficiency due to friction.